This invention relates to supported and bulk heterogeneous catalysts that are useful for catalyzing certain types of chemical reactions, the preparation of heterogeneous catalysts, and chemical reaction processes using heterogeneous catalysts.
Heterogeneous catalyst systems are employed in various commercially important chemical processes in the petroleum, petrochemical and chemical industries. In these processes, fluid reactants (liquid or gaseous) are contacted with a solid material exhibiting catalytic activity, with a catalyzed chemical reaction occurring at the interface between the fluid and solid phases. Heterogeneous catalyst systems typically comprise a carrier or support onto which a catalyst is deposited. The catalyst is typically in the form of a metal or metal-containing component that is deposited on the support surface using an impregnation or coating technique. Heterogeneous catalyst systems without a carrier or support are generally referred to as bulk catalysts. Bulk catalysts are typically prepared by co-precipitation techniques in which a catalytically active material and an inert material are substantially uniformly distributed throughout a composite solid material.
Generally the support material has a relatively low surface area making it unsatisfactory for achieving commercially acceptable overall production rates. However, to overcome this problem, a ceramic support is typically prepared by sintering a clay or other material at a high temperature to impart a desirable density and strength, and then the resulting ceramic support is coated with another material having a higher surface area. The catalytically active material is then deposited onto the higher surface area coating. A disadvantage with these heterogeneous catalyst systems having a higher surface area support phase (commonly referred to as a “washcoat”) disposed on a sintered lower surface area structural support is that the surface area of the coating tends to decrease during its service life due to erosion and/or thermal cycling in the reactor. Further, preparation of these supported catalysts requires two separate application steps, including first washcoating the carrier, then depositing the catalytically active material on the washcoat.
A problem with unsupported or carrierless heterogeneous catalyst systems that are coextruded with sinterable ceramic material and high surface area material is that they tend to be susceptible to thermal degradation at the elevated service temperatures typically employed during heterogeneous catalytic reaction processes. Moreover, catalyst effectiveness is reduced as compared with the supported catalysts and pressure drop tends to be undesirably high as compared with the supported catalysts.
Accordingly, it would be desirable to provide a method for coating an inert support material having a relatively low surface area with a composition that includes both a catalytically active material and a material that forms a high surface area phase on which the catalytically active material is dispersed. This would reduce the number of steps needed to prepare a supported heterogeneous catalyst and facilitate the preparation of supported catalysts exhibiting a very high effectiveness factor, but without the high pressure drop typically associated with packed bed reactors.
It would also be desirable to provide improved bulk phase heterogeneous catalysts that are prepared by extruding, injection molding or otherwise forming a mass of flowable material into a desired shape and solidifying the material to form a solid shape having a high surface area, porous structure on which a catalytically active material is distributed, and which exhibit an increased effectiveness factor.